In recent years, there have been total artificial hearts under development utilizing a wide variety of physical principles. Some of the artificial hearts utilize a Stirling engine, others use an electric torque motor with a pusher plate, others an electrical solenoid-driven pusher plate, others a pneumatically-powered sac, and still others an electric motor roller screw and cam.
One type of artificial heart under development is similar in principle to the well-known Jarvik 7 artificial heart, which has an artificial heart ventricle comprising a blood chamber and a gas chamber separated by a flexible diaphragm. The diaphragm is caused to flex by air alternately admitted to and exhausted from the air chamber.
This type of artificial heart must be powered wtih an "air driver." The standard device for driving the artificial heart accepts compressed air from a storage reservoir and manipulates it to provide a continuous series of air pressure pulses to each ventricle. The design of the conventional "air driver" permits independent control of the pressure intensity to the left and right ventricles. Also controllable is the duration of the pressure pulse (systole) and the time during pressure venting (diastole), both of which, taken together, determine the beats-per-minute.
The conventional "air driver" is not without its disadvantages. It is expensive, large and heavy, restricting a patient's degree of freedom and mobility. In addition, the conventional "air driver" requires electrical power for many of its operating elements. Thus, the conventional "air driver" is susceptible to electrical noise and interference, and must be shielded from water and combustible gases.
It is an object of the present invention to provide a fully-pneumatic drive circuit for an artificial heart of the type having a gas chamber and a blood chamber separated by a flexible diaphragm which is smaller, lighter and thus would provide a patient with a somewhat greater of degree of freedom and mobility than known heart drivers.
It is also an object of the invention to reduce the cost and complexity of the driver while maintaining performance and reliability by utilizing off-the-shelf, proven pneumatic digital logic elements.
The pneumatic drive circuit of the present invention requires no electrical components and therefore eliminates the need for electric power. This makes the circuit immune to power line noise and static electricity. Immersion in water does not effect it. And, since because it is pneumatic it cannot generate sparks, it is safe to operate in the presence of combustible vapors or gases.